Photophone



AU 33 EXAMINER 93 422569999 J/ c. L.. BROWN 2,466,000

PHOTOPHONE 2 Sheets-Sheet l ATTORNEY F I P B l0 6 Filed June 12, 1945 EXAM! NER April 5, 1949. C. 1 BROWN 2,466,000

' PHoToPHoNE Filed June 12, 1945 2 Sheets-Sheet 2 12 o SM2l L 51 f s 6 -5 i Y F163 g "5 i c X N39 52 535 z 28 50 a L 5o l CHESTER L. BROWN INVENTOR ATTORNEY Patented Apr. 5, 1949 UNITED STATES PATENT OFFICE Claims.

The present invention relates to certain new and useful improvements in a photophone and affords a compact device wherein the transmitter and its power source are housed in a conventional 5cel1 ashlight case; and the receiver is likewise housed in a similar flashlight case, the two flashlight cases being slidably and rotatably mounted on an expansible clamp which enables the transmitter and the receiver to be brought into the proper mouth and ear positions.

According to the present invention, the audio Wave is carried on a light beam derived from a filament lamp of the flashlight type and this filament is modulated by the audio current variations `produced by the microphone which is connected direct to the transformer without resorting to any intervening amplifier.

The invention is particularly directed to certain structural arrangements which afford a compact transmitter and receiver unit which can readily be carried about in constant readiness for instant use where two persons each equipped with the invention and in sight of each other, have need for two-way photophone communication. It is particularly serviceable for roof-toground conversation by city fire departments. It serves a similar purpose during construction of buildings. It is likewise serviceable for directing workers from a distance such as in excavations, or in bridge building, or in mines, quarries, etc.

The preferred form of the invention is shown in the accompanying drawings.

Fig. 1 is a sectional view of the transmitter and receiver coupled together by an expansible clamp.

Fig. 2 is a wiring diagram of the transmitter shown in Fig. 1.

Fig. 3 is a. plan view of the invention showing the transmitter and receiver slidably moved to their operating positions and spaced apart by expanding their connecting clamp.

Fig. 41s a Wiring diagram of the receiver shown in Fig. 1.

The transmitter is shown in Fig. 1 and Fig. 2 where it will be seen that thesecondary f of the transformer 6 is connected in series between the lamp 2 and battery S, and the primary g of this transformer 6 is connected in series between the microphone I2 and battery S. The switch X 2 is interposed between the battery and ground which is common to the lamp 2 and microphone I2.

Thus it will be seen that the D. C. current from the battery S passes through the secondary l to the lamp 2, and the A. C. current which is induced in the secondary f also flows to the lamp 2 to modulate the light therefrom in accordance with the audio current variations produced by the microphone I2. The primary g is made to match the impedance of the microphone; and the secondary f is made to match the impedance of the filament of the lamp 2. This impedance matching transformer 6 is fully sufficient to satisfactorily modulate the light emitted by the lamp 2 and no intervening amplifier is necessary.

Fig. 1 shows the physical embodiment of this transmitter, when housed in the 5cel1 flashlight case Y which is the preferred embodiment. The transformer 6 occupies the position which would normally be occupied by the forward battery, and only four batteries are used. Here the lamp 2, is mounted in a socket 3 which has its shell connected to the casing Y which here serves as ground, and the center contact connects to the secondary f of the transformer 6 which is here shown in diagram in the space which it occupies in the flashlight case Y. A spacer member 8 is provided with a central contact member 1 to which the secondary f is connected as is also the primary g. This Contact member 'I extends through the spacer member 8 so as to afford contact with the positive pole of the battery S'". The remaining batteries are arranged end to end in series, and the last battery S contacts a spring II which is mounted on the insulator I0. The line I4 connects this spring II to the insulated side of the switch X.

The microphone I2 is of the single button carbon granule type. As shown in Fig. 1 this microphone I2 is secured to the closure I6 which is threaded onto the flashlight case Y thus affording the necessary ground connection. The central button seats against a contact 9 in the insulator I0 and the line I5 connects this contact 9 with the primary g of the transformer 6. The spring II bears against the battery S and maintains the necessary contact, but unlike the usual ashlight, the spring II does not connect the negative pole of the battery S to ground, the line |4 and switch X are here used to establish that ground connection, so that this one switch closes the circuit for the microphone at the same time the lamp circuit is closed.

It will be noted that the outer ends of the wires I4 and l5 connect to the insulator disc l0 and there is suiicient slack in these wires to enable this insulator disc I to be lifted out whenever the microphone |2 is removed for the purpose of installing new batteries.

The lamp 2 is here shown with a reflector 4 and,

a plano glass however, a convex lens may be used if desired. It is necessary however that the emergent beam be sufciently divergent to form an illuminated area 12 or l5 feet in diameter at a distance of 100 yards, so that simple pointing of the transmitter will suffice, Without resorting to any sighting means.

The receiver portion of the invention is mounted in the fiashlight tube Z as shown in Fig. 1 and the circuit diagram is shown in Fig. 4.

These fiashlight tubes are conventionally made with an expanded portion W which is threaded so as to attach the forward end of the casing. This expanded portion is conventionally of surncient size to admit the photoelectric cell M which is of the cartridge type such as R. C. A. 921.

The receiver is a three tube, resistance coupled amplier and is carried on a chassis 2| which has brackets such as b secured thereto for mounting the tubes V in end to end relation, and an end bracket d is provided for mounting a jack 44 for connecting the receiver to its power source. This chassis 2| is transversely cupped so as to suitably fit within the tubular casing Y. This transverse cupping may be arcuate or else angular, either of which will suffice to stiifen the chassis longitudinally, as well as afford a proper t within the casing. The forward end of the chassis has a slotted end 22 which is offset to correspond to the expanded portion W. This slotted end 22 is to accommodate the seal-off tip conventional on this type of photoelectric cell M, the usual protector cap being discarded. This structure affords the necessary contact of the cathode 20 to ground. A plate member I8 is employed to connect the anode I9 to the receiver circuit, a suitable insulator I1 being employed to prevent grounding the anode.

For convenience of illustrating the end to end relationship of the amplifier tubes, the circuits are pictorially shown in Fig. 1 where the conventional seven contact base has the 4th and 5th contacts cut off, and the 6th and 7th contacts are shaded to indicate that they are on the far side from the 1st, 2nd and 3rd contacts. The 1st contact is here shown as bent over for convenience of connecting to the positive A voltage line. From this description the various contacts can readily be identified, and it is of course well known that the 1st and the (shaded) '7th contacts go to the two sides of the filament, the 2nd contact goes to the anode, the 3rd contact goes to the 2nd grid, and the (shaded) 6th contact goes to the 1st grid. It is of course well known that the 4th and 5th contacts are not needed for an IT4 vacuum tube such as here used. With this understanding, the circuits can readily be followed in Fig. 1 equally as well as in the diagram of Fig. 4.

The condenser E couples the anode I3 to the control grid of the first amplifier. The resistor 23 connects this same control grid to ground.

The positive A voltage from the battery 41 is fed from the jack 44 through the line 25 to the filament of each of the amplifiers, the opposite side of each filament being connected to ground as shown. The positive B voltage from the battery 41 is fed from the jack 44 through the line 4| to each of the amplifier tubes and to the photoelectric cell. The anode I9 is connected to the +B line 4| through the load resistor 26 and decoupling resistor 21, the latter being by-passed to ground by the decoupling condenser F so as to isolate the photoelectric cell M from the last amplifier stage.

Resistor 28 connects the screen grid of the first amplifier to the +B line 4|. This screen grid is by-passed to ground by the condenser H. The plate of the first amplifier tube, is connected to the +B line 4l by the load resistor 29 and decoupling resistor 30, the latter being by-passed to ground by condenser K. The condenser G couples the output of the rst amplifier tube to the control grid of the second amplifier, and this control grid is connected 4to ground by the resistor 3|.

The plate of the second amplifier is connected to the +B line 4| through load resistor 33 and decoupling resistor 34 the latter being by-passed to ground by the condenser R so as to isolate this amplifier from the final amplifier stage. Resistor 32 connects the screen grid of this second amplifier to the +B line 4I. This screen grid is by-passed to ground by condenser P. The condenser N couples the output of this second amplifier to the control grid of the final amplifier, and this control grid is connected to ground by the resistor 35 and also by-passed to ground by the condenser I which eliminates the high audio frequencies.

The plate of the final amplifier is connected to the +B line 4| through load resistor 31. The resistor 36 connects the screen grid of this final amplifier to +B line 4| and this screen grid is bypassed to ground by condenser U. The condenser T couples the output of this final amplifier to the earphone 39, the plug 42 and jack 43 being employed for convenience of removing the assembled receiver from the flashlight casing Z. The earphone 39 is mounted upon the casing by brackets 38 and suitably grounded to the casing as indicated at 40.

As seen in Fig. 1, this three stage amplifier can readily be housed in a flashlight casing of the same size as that previously described for housing the transmitter, and as here shown, the convex lens L is employed to condense the received light beam upon the cathode 20 so as to afford increased intensity. It is unnecessary to focus the light beam upon the cathode and therefore the lens L may have a longer focal length than its distance from the cathode 20. As here shown the jack 44 is secured to the bracket d and then passes through the center of the cap 43 which is screw threaded onto the ashlight casing, this structure sumcing to hold the chassis 2| and its brackets 6 in proper position within the tubular casing Z.

The described structural arrangement is of consequence and importance in the original assembly of the receiver and any subsequent disassembly for replacement or repair. As here shown. the photoelectric cell M can readily be removed through the forward end of the flashlight by first removing the lens L. 'I'he rear cap 48 is then removed and the chassis 2| is pulled out sufciently to remove the plug 42 from the jack 43, whereupon the chassis 2| can be removed. It

will be noted that no tools are required for this removal nor for again inserting the parts in assembled position.

As shown in Fig. 1 and Fig. 3 these two ashlight casings Y and Z are connected together by the expansible clamp C which has two intergaging parts 50 and 5l which are slidably engaged with each other. As here shown, the part has a lip 52 on each of its opposite edges and these lips form guideways in which the part 50 is slidably mounted. These slidable parts 5U and 5I are provided with corresponding slots 53 and 54 through which a thumb screw 55 is mounted to hold the parts in set relation.

As best seen in Fig. 3 the part 50 has a curved portion 50 which iits around the tubular casini,r Z and the part 5I has a curved portion 5|' which ts around the tubular casing Y. These curved portions 50 and 5|' embrace slightly more than half the circumference of these tubular casings and are sufiiciently resilient so that they can be snapped on and olf whenever it is desired to separate the transmitter and receiver from each other. These curved portions frictionally engage the tubular casings so that they are longitudinally slidable therein and can readily be brought into the required mouth and ear positions by pushing the transmitter casing Y forwardly and pulling the receiver casing Z rearwardly according to the requirements of the individual operator, and the expansible clamp C enables the two casingsl Y and Z to be suitably spaced apart in parallel relation, so that when the transmitter is directed towards the receiver of another operator, the transmitter of the latter will also be directed towards the receiver of the former in immediate readiness for two-way cornmunication.

The device is suiiiciently small to be readily carried about and can readily be attached to the belt strap of the user. The entire equipment is contained in the two flashlight cases, with the exception of the battery 41 which can conveniently be carried on the belt strap of the user.

In the operation of the invention, the two flashlight cases are spaced apart and slidably moved to the positions shown in Fig. 3 so that the microphone l2 and earphone 39 will be in proper relationship for the mouth and ear of the operator. The battery 41 is plugged in and the operator makes known his intention to communicate by using the switch X to give any suitable flash signal while pointing the transmitter tube towards a second operator with whom he desires to communicate. The second operator then places his photophone in pro-per mouth and ear positions and answers by using his switch X to give a suitable flash signal. These iiash signals aiTord a convenient guide to enable each operator to properly direct his transmitter merely .by pointing it` without resorting to any sighting means. The switch X is kept closed while using the transmitter, and two-way communication is had without resorting to any switching. Each operator may alternately turn towards any other operator and communicate with each of them individually, without being heard by more than one at a time.

It will be seen that the invention provides a compact, lightweight photophone which is very inexpensive and requires no skill to operate.

I claim as my invention:

l. A photophone comprising a tubular flashlight casing having a filament lamp and reflector disposed so as to direct light forwardly in line with the axis of said casing, a microphone 0n the rear end of said casing, a series of batteries in end-to-end relation within said casing, a transformer within said casing and having its primary in series between said microphone and said batteries and having its secondary in series between said lamp and said batteries, circuit connectons including a switch for connecting said batteries to said lamp and said microphone, a second tubular casing having a convex lens in the forward end thereof, a photoelectric cell spaced rearwardly of said lens, an amplifier within said second casing and in circuit with said photoelectric cell, an earphone laterally disposed upon said second casing and in circuit with said amplifier, and means for holding said casings in spaced apart parallel relation with said microphone disposed more forwardly than said earphone.

2. A photophone comprising a pair of tubular casings, an expansible clamp wherein said tubular casings are slidably and rotatably mounted in spaced apart parallel relation, a light projecting transmitter in one of said casings, an amplifying receiver in the other of said casings, said transmitter having its microphone located on the rear end of its casing and said receiver having an earphone mounted on the side of its caslng.

3. A photophone comprising a pair of tubular casings, an expansible clamp wherein said tubular casings are slidably and rotatably mounted in spaced apart parallel relation, a microphone mounted on the rear end of one of said tubular casings, a lament lamp and a reflector mounted in the forward end of said casing, a series of batteries arranged in end-to-end relation within said casing, a transformer having its primary coil connected in series between said microphone and said batteries and having its secondary coil connected in series between said lamp and said batteries, a switch for connecting said batteries to said lamp and said microphone, a photoelectric cell mounted in the forward end of the other of said tubular casings, a lens for condensing light upon said photoelectric cell, an amplifier mounted within the latter casing and in circuit with said photoelectric cell, an earphone in circuit with said amplifier, and a jack in the rear end of the latter casing for connecting said amplifier to a power supply.

4. In a photophone, a transmitter comprising a tubular casing, a single button carbon granule microphone mounted on one end of said casing, a filament lamp mounted at the opposite end of said casing, a series of batteries disposed in end-to-end relation within said casing, a transformer within said casing, said transformer having its primary directly connected in series between said microphone and said batteries, said transformer having its secondary directly connected in series between said lamp and said batteries, said lamp and said microphone being connected to a common ground, a switch mounted on said casing and connecting said batteries to the common ground, said lamp having a reflector directing the light outwardly along the axis line of said tubular casing.

5. In a photophone, a transmitter comprising a tubular iiashlight casing having a filament lamp and a reflector axially disposed therein, a transformer mounted behind said lamp and having its secondary connected thereto, a disc having a. central contact button connected in common to the primary and secondary of said transformer, a series of batteries arranged in end-to-end relation within said casing and having a contact n i n REFERENCES CITED The following references are of record 1n the le of this patent:

UNITED STATES PATENTS Number Name Date 796,254 Hartmann Aug. 1, 1905 1,973,089 Mechau Sept. 11, 1934 2,153,709 Bournislen Apr. 11, 1939 2,389,649 Stark et al Nov. 27, 1945 OTHER REFERENCES Radio Craft, The Skin-Effect Talking Lightbeam by Gerald Mosteller, January 1939; pp. 411,466.

QST, A Simple Light-Beam Communication System by James B. Stevens and Eleanor C. Stevens, May 1942, pp. 13, 14, 98, 100. 

